The invention relates to a liquid atomizing process and apparatuses, namely apparatuses and processes used in conjunction with fluid catalytic cracking (FCC) processes that require high fluid throughput and low pressure drop. The process comprises forming a two-phase fluid mixture of the hot feed oil and a dispersion gas, such as steam, dividing the fluid mixture into two separate streams which are passed under pressure through an impingement mixing zone, a shear mixing zone to recombine the streams into a single stream which passes into a lower pressure atomization zone, where atomization occurs to form a spray of atomized liquid droplets.
Fluid atomization is well known and used in a wide variety of applications and processes, including aerosol sprays, the application of pesticides and coatings, spray drying, humidification, mixing, air conditioning, and chemical and petroleum refinery processes. In many applications, a pressurized fluid (with or without the presence of an atomizing agent) is forced through an atomization nozzle having a relatively small orifice. Atomization occurs at the downstream side of the orifice, and the degree of atomization is determined by the orifice size, the pressure drop across the orifice, fluid density, viscosity, and surface tension. Atomization is increased and the droplet size is decreased with decreasing orifice size and increasing pressure drop.
Increasing the degree of atomization of relatively viscous fluids at high flow rates is particularly challenging, especially for the heavy petroleum oil feeds that may be used in FCC processes. FCC processes are widely used in the petroleum refining industry primarily for converting high-boiling petroleum oils to more valuable lower-boiling products including gasoline and middle distillates such as kerosene, jet and diesel fuel, and heating oil.
In FCC processes, a preheated feed is often mixed with an atomization promoting fluid, such as steam, to assist in the atomization of the feed. The atomized feed contacts a particulate, hot cracking catalyst flowing up through a riser which comprises the FCC reaction zone. Smaller oil feed droplet sizes in the reaction zone result in more feed conversion to valuable products, particularly with the incorporation of heavy feed material, such as a resid, into the FCC feed. In some instances, feed material that does not contact the uprising catalyst particles thermally cracks primarily to methane and cokexe2x80x94generally undesirable products. Consequently, efforts continue to try to find economically viable means to decrease the droplet size of the atomized oil, preferably without an unacceptably high pressure drop through the atomizer or nozzle and/or without increasing the amount of steam or other atomization promoting agent. Examples of such efforts are disclosed in U.S. Pat. Nos. 5,289,976 and 5,173,175, which disclose an average feed droplet size in the range of about 400-1000 microns. There is still a need for finer atomization of the heavy oil feed for the FCC process and of other fluids for other processes as well. It would be particularly beneficial if the atomized liquid droplet size could be reduced to less than 300 microns.
One embodiment of the present invention comprises a liquid atomization apparatus comprising a body comprising a fluid inlet and a fluid outlet and configured to define an impingement mixing zone and a shear mixing zone. The zones are positioned between the inlet and the outlet. The fluid inlet comprises a splitter that can split an incoming fluid stream into at least two streams. The impingement mixing zone comprises at least one impingement surface configured to impinge at least a portion of one fluid stream against another impinged stream wherein the included angle between two impinged streams is between about 120xc2x0 and 240xc2x0. The shear mixing zone has a cross-sectional area defined by a first dimension and a second dimension, wherein the first dimension decreases along a longitudinal axis through the body in a direction toward the fluid outlet.
Another embodiment of the present invention comprises a liquid atomization apparatus comprising a body comprising at least one fluid inlet, at least one fluid outlet, and a fluid passageway extending between the inlet and the outlet. The passageway defines an impingement mixing and a shear mixing zone downstream from the impingement mixing zone. The passageway also defines at least one impingement surface configured to be substantially perpendicular to a longitudinal axis extending through the body. The impingement surface is configured to impart radially inward flow (in a direction normal to the overall flow direction) to a portion of fluid flowing through the passageway. The shear mixing zone has a cross-sectional area defined by a first dimension and a second dimension, wherein the first dimension decreases along a longitudinal axis through the body in a direction toward the fluid outlet.
Another embodiment of the present invention comprises a process for forming a spray of liquid droplets comprising the steps of: (a) forming at least two streams of a two-phase fluid comprising a gas phase and a liquid phase; (b) passing the streams to an impingement mixing zone wherein at least a portion of each stream is impinged against at least a portion of another stream and wherein the included angle between the impinged streams is between about 170xc2x0 and 190xc2x0 to form a single mixed stream; (c) passing the single mixed stream to a shear mixing zone and imparting shear mixing forces to the single mixed stream to form a shear mixed stream; and, (d) passing the shear mixed stream to an atomizing zone wherein the gas phase expands and increases the surface area of the liquid phase, thereby producing a spray of liquid droplets.
Another embodiment of the present invention comprises a process for forming a spray of liquid droplets comprising the steps of: (a) forming a plurality of streams of a two-phase fluid comprising a gas phase and a liquid phase; (b) impinging at least a portion of each stream against at least a portion of another stream to form a single mixed stream, wherein the included angle between the impinged streams is between about 120xc2x0 and 240xc2x0; (c) subjecting the single mixed stream to shear mixing forces, thereby forming a shear mixed stream; and, (d) expanding the gas phase in the shear mixed stream, thereby producing a spray of liquid feed droplets.
Another embodiment of the present invention comprises a catalytic cracking process comprising the steps of: (a) forming at least two streams of a two-phase fluid comprising a gas phase and a liquid phase, the liquid phase comprising a FCC feed; (b) passing the streams to an impingement mixing zone wherein at least a portion of each stream is impinged against at least a portion of another stream and wherein the included angle between the impinged streams is between about 120xc2x0 and 240xc2x0, thereby forming a single mixed stream; (c) passing the single mixed stream to a shear mixing zone and imparting shear mixing forces to the single mixed stream to form a shear mixed stream; (d) passing the shear mixed stream to an atomizing zone wherein the gas phase expands and increases the surface area of the liquid phase, thereby producing a spray of liquid feed droplets; (e) passing the spray of liquid feed droplets into a FCC reaction zone; and, (f) contacting the liquid feed droplets with a catalytic cracking catalyst under catalytic cracking conditions. In one embodiment the impingement zone and the shear mixing zone are contained within an embodiment of a nozzle described herein.
Another embodiment of the present invention comprises a catalytic cracking process comprising the steps of: (a) forming a plurality of streams of a two-phase fluid comprising a gas phase and a liquid phase, the liquid phase comprising a FCC feed; (b) impinging at least a portion of each stream against at least a portion of another stream to form a single mixed stream, wherein the included angle between the impinged streams is between about 170xc2x0 and 190xc2x0; (c) subjecting the single mixed stream to shear mixing forces, thereby forming a shear mixed stream; (d) expanding the gas phase in the shear mixed stream, thereby producing a spray of liquid feed droplets; and, (e) contacting the liquid feed droplets with a catalytic cracking catalyst under catalytic cracking conditions.
In each process and/or apparatus of the present invention, the included angle between the impinged streams is more preferably between about 175xc2x0 and about 180xc2x0, most preferably about 180xc2x0.